Patent application title: ELECTROSTATIC COATING DEVICE

Abstract:

An atomizer (1) which is composed of an air motor (2) and a rotary
atomizing head (3) is mounted in a front side of a housing member (9),
outer surfaces (9A) of which are covered in a cover member (10). Further,
a high voltage discharge electrode assembly (15) is provided around a
front side of the housing member (9), with outer periphery of the cover
member (10) circumvented by a blade ring (17) of the high voltage
discharge electrode assembly (15). An edge portion (19) in the shape of a
thin blade is provided at a projected rear end of the blade ring (17).
Thus, electric field is concentrated at the edge portion (19) to induce a
corona discharge on and around entire blade ring (17).

Claims:

1. An electrostatic coating apparatus comprised of a paint atomizing means
adapted to spray atomized paint particles toward a work piece, a housing
member formed of an electrically insulating material to accommodate said
paint atomizing means in position, a high voltage application means for
imparting a high voltage electrostatic charge to paint particles sprayed
by said paint atomizing means for electrostatic deposition on said work
piece, and a corona ring formed in the shape of a ring circumventing said
housing member and applied with a high voltage from said high voltage
application means to induce corona discharges, characterized in that said
electrostatic coating apparatus comprises:said corona ring having a blade
ring projected at least in axially forward, axially rearward, radially
inward or radially outward of said housing member, said blade ring being
gradually reduced in thickness toward a projected end in the fashion of a
thin blade, providing a sharp edge portion all around said blade
ring;said blade ring discharging a high voltage continuously
substantially on and around entire edge portion.

2. An electrostatic coating apparatus as defined in claim 1, wherein a
number of notches are provided at intervals along said edge portion of
said blade ring.

3. An electrostatic coating apparatus comprised of a paint atomizing means
adapted to spray atomized paint particles toward a work piece, a housing
member formed of an electrically insulating material to accommodate said
paint atomizing means in position, a high voltage application means for
imparting a high voltage electrostatic charge to paint particles sprayed
by said paint atomizing means for electrostatic deposition on said work
piece, and a corona ring formed in the shape of a ring circumventing said
housing member and applied with a high voltage from said high voltage
application means to induce corona discharges, characterized in that said
electrostatic coating apparatus comprises:said corona ring constituted by
a star ring formed in the shape of a star by bending a wire alternately
in radially inward and outward directions toward and away from said
housing member; andsaid star ring discharging a high voltage continuously
substantially on and around entire parts thereof.

4. An electrostatic coating apparatus comprised of a paint atomizing means
adapted to spray atomized paint particles toward a work piece, a housing
member formed of an electrically insulating material to accommodate said
paint atomizing means in front edge portion, a high voltage application
means for imparting a high voltage electrostatic charge to paint
particles sprayed by said paint atomizing means for electrostatic
deposition on said work piece, and a corona ring formed in the shape of a
ring circumventing said housing member and applied with a high voltage
from said high voltage application means to induce corona discharges,
characterized in that said electrostatic coating apparatus comprises:said
corona ring constituted by a helical ring formed by helically winding a
wire into the shape of a circular endless coil; andsaid helical ring
discharging a high voltage continuously substantially on and around
entire parts thereof.

5. An electrostatic coating apparatus as defined in claim 3, wherein said
wire has a diameter between 0.3 mm and 5 mm.

6. An electrostatic coating apparatus as defined in claim 4, wherein said
wire has a diameter between 0.3 mm and 5 mm.

Description:

[0001]An atomizer including an air motor and a rotary atomizing head is
mounted in a front side of a housing member, outer surfaces of which are
covered in a cover member. Further, a high voltage discharge electrode
assembly is provided around a front side of the housing member, with an
outer periphery of the cover member circumvented by a blade ring of the
high voltage discharge electrode assembly. An edge portion in the shape
of a thin blade is provided at a projected rear end of the blade ring.
Thus, an electric field is concentrated at the edge portion to induce a
corona discharge on and around the entire blade ring.

TECHNICAL FIELD

[0002]This invention relates to an electrostatic coating apparatus which
is adapted to spray paint under application of a high voltage.

BACKGROUND ART

[0003]Generally, as an electrostatic coating apparatus, for example, there
have been known paint coating apparatus which are constructed of an
atomizer consisting of an air motor and a rotary atomizing head, a
housing member adapted to hold the air motor of the atomizer, and a high
voltage generator adapted to impart a negative high voltage electrostatic
charge to sprayed paint particles (e.g., see, for example, Japanese
Patent Laid-Open No. H10-57848 and Japanese Utility Model Laid-Open No.
H3-75856).

[0004]In the case of prior art electrostatic coating apparatuses of the
sort mentioned above, an electrostatic field is formed by lines of
electric force between a rotary atomizing head which apply a negative
high voltage electrostatic charge and a work piece. In this state, if the
rotary atomizing head is put in high speed rotation to spray paint,
sprayed paint particles which have been sprayed from a rotary atomizing
head are electrostatically charged to become charged paint particles
which are imparted with a negative high voltage electrostatic charge.
Thus, charged paint particles are urged to fly toward and deposit on
surfaces of a work piece which is connected to the earth.

[0005]Further, according to the prior art, repulsive electrodes are
located on an outer peripheral side of a housing member, and a high
voltage of the same polarity as charged paint particles is applied to the
repulsive electrodes. By a repulsion force which occurs between a
repulsive electrode and charged paint particles, the latter are urged to
fly toward a work piece and prevented from depositing on the housing
member.

[0006]In the case of electrostatic coating apparatuses disclosed in
above-mentioned Japanese Patent Laid-Open No. H10-57848 and Japanese
Utility Model Laid-Open No. H3-75856, a repulsive electrode which is
located around the outer periphery of a housing member has a repulsion
force effective against charged paint particles but not effective enough
against electrostatically attenuated paint particles floating around a
housing member and carrying only an attenuated quantity of electrostatic
charge.

[0007]Further, in the case of electrostatic coating apparatus in Japanese
Patent Laid-Open No. H10-57848 and Japanese Utility Model Laid-Open No.
H3-75856, in order to prevent spark discharges between a repulsive
electrode and a grounded body, the repulsive electrode is formed in the
shape of a ring or ball with smooth surfaces to avoid concentration of
electric field. Therefore, the repulsive electrode is incapable of
supplying a sufficient quantity of discharge ions to outer surfaces of a
housing member, resulting in failure in maintaining a high voltage
electrostatic potential on outer surfaces of the housing member.

[0008]As a consequence, as an electrostatic coating operation is
continued, paint particles start to gradually deposit on outer surfaces
of the housing member and remain there as paint deposits. Such paint
deposits give rise to a problem of degradations in insulation quality of
outer surfaces of the housing member.

[0009]On the other hand, in order to maintain a housing member at a high
voltage electrostatic potential, for example, there may be employed a
repulsive electrode of a larger diameter to broaden high voltage
discharge surface areas. However, in this case, there is a necessity for
keeping the repulsive electrode at a sufficient distance from a work
piece to prevent spark discharges which might occur between the repulsive
electrode and a work piece or other grounded body since a high voltage is
constantly applied to the repulsive electrode.

[0010]Therefore, in addition to degradations in performance quality, an
operative range of an atomizer is narrowed by the use of a repulsive
electrode of a large outside diameter. Especially, in a case where a
coating operation is carried out in a narrow space like inside of vehicle
body, difficulties are encountered in keeping a distance between a
repulsive electrode and a grounded body like a vehicle body, and a
coating operation becomes infeasible.

DISCLOSURE OF THE INVENTION

[0011]In view of the above-discussed problems with the prior art, it is an
object of the present invention to provide an electrostatic coating
apparatus with a high voltage discharge electrode which is reduced in
size but has broadened high voltage discharge area.

[0012](1) In order to solve the above-discussed problems, the present
invention is applied to an electrostatic coating apparatus comprised of a
paint atomizing means adapted to spray atomized paint particles toward a
work piece, a housing member formed of an electrically insulating
material to accommodate the paint atomizing means in position, a high
voltage application means for imparting a high voltage electrostatic
charge to paint particles sprayed by the paint atomizing means for
electrostatic deposition on the work piece, and a corona ring formed in
the shape of a ring circumventing the housing member and applied with a
high voltage from the high voltage application means to induce corona
discharges.

[0013]The electrostatic coating apparatus according to the present
invention is characterized in that the corona ring comprises: a blade
ring projected at least in axially forward, axially rearward, radially
inward or radially outward of the housing member, the blade ring being
gradually reduced in thickness toward a projected end in the fashion of a
thin blade, providing a sharp edge portion all around the blade ring; the
blade ring discharging a high voltage continuously substantially on and
around entire edge portion.

[0014]As described above, as a corona ring, the electrostatic coating
apparatus employs a blade ring with an edge portion which is projected
toward a sharp edge in fashion of a thin blade. Therefore, electric field
is concentrated at the edge portion, inducing corona discharge on and
around entire blade ring, and a sufficient amount of discharge ions can
be supplied to the housing member to maintain a high voltage
electrostatic potential on outer surfaces of the housing member.

[0015]Further, the corona discharges at the edge portion of the blade ring
contribute to recharge electrostatically attenuated paint particles. As a
consequence, a repulsion force occurs between recharged paint particles
and the blade ring or housing member, preventing deposition of paint
particles on the housing member in an assured manner.

[0016]Furthermore, by the use of the edge portion of the blade ring, a
corona discharge can be induced on and around the entire body of the
annular blade ring which circumvents the housing member. Therefore, it
becomes possible to downsize the blade ring as compared with a case where
corona discharge is induced only part of a blade ring, permitting to
secure a sufficient distance between the blade ring and a work piece to
prevent spark discharges which would otherwise occur between the blade
ring and a work piece, while broadening a range of movement of the
atomizer even at the time of an operation in a narrow space to ensure
higher performances.

[0017](2) In this instance, according to the present invention, a number
of notches may be provided at intervals along the edge portion of the
blade ring.

[0018]With the arrangements just described, an electric field can be
concentrated at opposite ends of the notches in the circumferential
direction of the blade ring to let discharges take place more easily at
opposite ends of the notches, thereby accelerating corona discharges by
the blade ring.

[0019](3) According to a feature of the present invention, the corona ring
is constituted by a star ring formed in the shape of a star by bending a
wire alternately in radially inward and outward directions toward and
away from the housing member; the star ring discharging a high voltage
continuously substantially on around entire parts thereof.

[0020]In case the corona ring is constituted by a star ring in the shape
of a star which is formed by bending a wire at a plural number of points,
further intensifying concentration of an electric field at bent portions
of the ring. Accordingly, a discharge take place more easily at bent
portions of the ring to accelerate corona discharges at the respective
bent portions.

[0021]Furthermore, in case the wire diameter of the star ring is reduced,
concentration of electric field on the entire star ring can be
intensified and corona discharges can be induced continuously. Therefore,
a sufficient amount of discharge ions can be supplied to the housing
member to maintain a high voltage electrostatic potential on outer
surfaces of the housing member.

[0022]Further, the corona discharges from the star ring contribute to
recharge electrostatically attenuated paint particles. As a consequence,
a repulsion force occurs between recharged paint particles and the star
ring or housing member, preventing deposition of paint particles on the
housing member in an assured manner.

[0023]Furthermore, as a corona discharge is induced on and around the
entire star ring, it becomes possible to downsize the star ring as
compared with a case where corona discharge is induced only part of a
star ring, permitting to secure a sufficient distance between the star
ring and a work piece to prevent spark discharges which would otherwise
occur between the star ring and a work piece, while broadening a range of
movement of the atomizer even at the time of an operation in a narrow
space to ensure higher performances.

[0024](4) According to another feature of the present invention, the
corona ring is constituted by a helical ring formed by helically winding
a wire into shape of a circular endless coil; the helical ring
discharging a high voltage continuously substantially on and around
entire parts thereof.

[0025]In this case, the corona ring is constituted by a helical ring which
is helically wound into the shape of an endless circular coil. The
helical ring can be downsized in outer configuration, and can be
increased in total length of the wire. In case the wire diameter of the
helical ring is reduced, concentration of electric field on the entire
helical ring can be intensified and corona discharges can be induced
continuously. Therefore, as corona discharge can be induced on the entire
helical ring which is long size in total, a sufficient amount of
discharge ions can be supplied to the housing member to maintain a high
voltage electrostatic potential on outer surfaces of the housing member.

[0026]Further, the corona discharges from the helical ring contribute to
recharge electrostatically attenuated paint particles. As a consequence,
a repulsion force occurs between recharged paint particles and the
helical ring or housing member, preventing deposition of paint particles
on the housing member in an assured manner.

[0027]Furthermore, as a corona discharge is induced on and around the
entire helical ring, it becomes possible to downsize the helical ring as
compared with a case where corona discharge is induced only part of a
helical ring, permitting to secure a sufficient distance between the
helical ring and a work piece to prevent spark discharges which would
otherwise occur between the helical ring and a work piece, while
broadening a range of movement of the atomizer even at the time of an
operation in a narrow space to ensure higher performances.

[0028](5) In this instance, according to the present invention, the wire
has a diameter between 0.3 mm and 5 mm.

[0029]Consequently, the electric field around the wire can be intensified
to induce a corona discharge continuously on and around the entire corona
ring, supplying a sufficient amount of discharge ions to the housing
member while recharging electrostatically attenuated paint particles.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]In the accompanying drawings:

[0031]FIG. 1 is a longitudinal sectional view of a rotary atomizing head
type coating apparatus according to a first embodiment of the present
invention;

[0032]FIG. 2 is a fragmentary longitudinal section showing an atomizer of
FIG. 1 and surrounding parts on an enlarged scale;

[0033]FIG. 3 is a right-hand side view of a high voltage discharge
electrode assembly shown in FIG. 1, taken in the direction of arrows
III-III of FIG. 1;

[0034]FIG. 4 is a perspective view of the high voltage discharge electrode
assembly of FIG. 1 alone;

[0035]FIG. 5 is a front view of a rotary atomizing head type coating
apparatus according to a second embodiment of the invention;

[0036]FIG. 6 is an enlarged front view of the coater unit of FIG. 5, with
a cover member cut away to show inner components;

[0037]FIG. 7 is a longitudinal sectional view of the coater unit of FIG.
5;

[0038]FIG. 8 is a left-hand side view of the coater unit of the second
embodiment shown in FIG. 6;

[0039]FIG. 9 is a cross-sectional view of a high voltage discharge
electrode assembly alone, taken in the direction of arrows IX-IX of FIG.
8;

[0040]FIG. 10 is a perspective view of the high voltage discharge
electrode assembly of FIG. 8;

[0041]FIG. 11 is a left-hand side view similar to FIG. 8, showing a rotary
atomizing head type coating apparatus according to a third embodiment of
the invention;

[0042]FIG. 12 is a cross-sectional view of a high voltage discharge
electrode assembly alone, taken in the direction of arrows XII-XII of
FIG. 11;

[0043]FIG. 13 is a perspective view of the high voltage discharge
electrode assembly of FIG. 11 alone;

[0044]FIG. 14 is a front view similar to FIG. 6, showing a rotary
atomizing head type coating apparatus according to a fourth embodiment of
the invention, with a cover member cut away to show inner components;

[0045]FIG. 15 is a left-hand side view similar to FIG. 8, showing a rotary
atomizing head type coating apparatus according to a fourth embodiment of
the invention;

[0046]FIG. 16 is a perspective view of a high voltage discharge electrode
assembly of FIG. 15 alone;

[0047]FIG. 17 is a schematic illustration explanatory of positional
relations between a star ring and a work piece;

[0048]FIG. 18 is a left-hand side view similar to FIG. 8, showing a rotary
atomizing head type coating apparatus according to a fifth embodiment of
the invention;

[0049]FIG. 19 is a perspective view of a high voltage discharge electrode
assembly of FIG. 18 alone; and

[0050]FIG. 20 is an enlarged cross-sectional view of a helical ring, taken
in the direction of arrows XX-XX of FIG. 18.

BEST MODE FOR CARRYING OUT THE INVENTION

[0051]Hereafter, with reference to the accompanying drawings, the present
invention is described more particularly by way of its preferred
embodiments which are applied by way of example to a rotary atomizing
head type coating apparatus as an electrostatic coating apparatus.

[0052]Referring first to FIGS. 1 to 4, there is shown a first embodiment
of the present invention. Referring to the drawings, indicated at 1 is an
atomizer for spraying paint particles toward a work piece (not shown)
which is held at the ground potential. This atomizer 1 is constituted by
an air motor 2 and a rotary atomizing head 3, which will be described
hereinafter.

[0053]Indicated at 2 is an air motor which is formed of a conducting
metallic material. This air motor 2 is constituted by a motor housing 2A,
a hollow rotational shaft 2C rotatably supported within the motor housing
2A through air bearing 2B, and an air turbine 2D which is fixedly
provided on a base end portion of the rotational shaft 2C. Upon supplying
drive air to the air turbine 2D, the rotational shaft 2C of the air motor
2 is put in high speed rotation, for example, rotated at a speed of 3,000
to 100,000 r.p.m. together with the rotary atomizing head 3.

[0054]Denoted at 3 is a rotary atomizing head which is mounted on a fore
end portion of the rotational shaft 2C of the air motor 2. This rotary
atomizing head 3 is formed of, for example, a conducting metallic
material or a conducting synthetic resin material. After putting the
rotary atomizing head 3 in high speed rotation by the air motor 2, paint
is supplied thereto through a feed tube 4, which will be described
hereinafter, whereupon supplied paint is sprayed from releasing edges 3A
at the fore end of the rotary atomizing head 3 under the influence of
centrifugal force. Further, the rotary atomizing head 3 is connected to a
high voltage generator 7 through the air motor 2. Therefore, during an
electrostatic coating operation, a high voltage is applied to the rotary
atomizing head 3 as a whole, and a high voltage is directly charged to a
paint flowing on surfaces of the rotary atomizing head 3.

[0055]Designated at 4 is a feed tube which is passed through the
rotational shaft 2C. Fore end of the feed tube 4 is projected out of the
fore end of the rotational shaft 2C and extended into the rotary
atomizing head 3. A paint passage 5 which is provided internally of the
feed tube 4 is connected to a paint supply source and a thinner supply
source (both not shown) through a color changing valve device. A valve
seat 4A is provided at a longitudinally intermediate portion of the feed
tube 4 for seating and unseating a valve member 6A. Thus, the feed tube 4
is used to supply a paint from the paint supply source to the rotary
atomizing head 3 through the paint passage 5 during a coating operation,
and to supply a wash or cleaning fluid (thinner, air and so forth) from
the thinner supply source at the time of a cleaning operation or at the
time of color change.

[0056]In place of the feed tube 4 adopted in the present embodiment, there
may be employed a feed tube of a double tube construction which has a
paint passage internally of an inner tube and a thinner or cleaning fluid
passage internally of an outer tube. Further, instead of providing the
paint passage 5 internally of the feed tube 4 as in the present
embodiment, there may be employed a paint passage of a different shape or
of different routing depending upon the type of the atomizer 1.

[0057]Indicated at 6 is a paint supply valve, for example, a normally
closed valve, which is provided within the length of the paint passage 5.
This paint supply valve 6 is constituted by a valve body 6A which is
extended internally of the paint passage 5 and provided with a fore end
portion to be seated on and unseated from the valve seat 4A, a piston 6C
which is provided at the base end of the valve body 6A and slidably
fitted in a cylinder 6B, a valve spring 6D which is provided within the
cylinder 6B to bias the valve body 6A in a closing direction, and a
pressure receiving chamber 6E which is provided in the cylinder 6B on the
opposite side of the piston 6C away from the valve spring 6D. As soon as
drive air (a pilot air pressure) is introduced into the pressure
receiving chamber 6E, the valve body 6A is moved in an opening direction
against the action of the valve spring 6D to permit a paint flow through
the paint passage 5.

[0058]Indicated at 7 is a high voltage generator which is connected to the
air motor 2 to serve as a high voltage application means. This high
voltage generator 7 is constituted by a multi-stage rectification circuit
(the so-called Cockcroft circuit) which is constituted by a plurality of
capacitors and diodes (both not shown). By the high voltage generator 7,
a DC source voltage which is supplied from a high voltage controller 8 is
elevated to generate a high voltage, for example, a high voltage in the
range of -30 to -150 kV. At this time, output high voltage to be
generated by the high voltage generator 7 is determined by the source
voltage supplied from the high voltage controller 8. That is to say, the
output voltage (a high voltage) of the high voltage generator 7 is
controlled by the high voltage controller 8. Through a high voltage cable
7A, the high voltage generator 7 is connected to the air motor 2 and the
rotary atomizing head 3 for directly charging paint with a high voltage
by the rotary atomizing head 3.

[0059]Denoted at 9 is a housing member which is adapted to accommodate the
air motor 2 and high voltage generator 7. This housing member 9 is formed
substantially in a cylindrical shape by the use of an electrically
insulating synthetic resin material, for example, such as POM
(polyoxymethylene), PET (polyethylene terephthalate), PEN (polyethylene
naphthalate), PP (polypropylene), HP-PE (high-pressure polyethylene),
HP-PVC (high-pressure polyvinylchloride), PEI (polyether imide), PES
(polyether sulfon), polymethyl pentene and the like.

[0060]The housing member 9 is provided with a cylindrical outer surface 9A
on its outer peripheral side and a flanged large diameter rear end
portion 9B at its rear end. A motor receptacle hole 9C is provided in a
fore end portion of the housing member 9 to accommodate the air motor 2
therein, while a generator receptacle hole 9D provided in a rear end
portion of the housing member 9 to accommodate the high voltage generator
7 therein.

[0061]Denoted at 10 is a cover member which is formed in a tubular shape
to enshroud the housing member 9 in radially spaced relation with the
outer surface 9A of the latter. This cover member 10 is formed of an
electrically insulating and non-water-absorptive synthetic resin material
with high insulating properties, for example, an electrically insulating
synthetic resin material such as PTFE (polytetrafluoroethylene), POM
(polyoxymethylene) or PET (polyethylene terephthalate) with surfaces
treated with a water repellent agent and the like. Further, the cover
member 10 is formed in a tubular shape and has a small wall thickness
which is, for example, in the range of 0.1 mm to 5 mm for the sake of
mechanical strength. Further, provided at the fore end of the cover
member 10 is a front closing member 11 which is extended radially inward
in such a way as to close the front end of the housing member 9.

[0062]In this instance, rear end of the cover member 10 is fixed on the
flanged large diameter rear end portion 9B at the rear end of the housing
member 9, while fore end of the cover member 10 is fixed around the front
closing member 11. However, except the fixed fore and rear ends,
substantially the entire inner peripheral surface of the cover member 10
is disposed to confront outer peripheral surface of the housing member 9
in a radially spaced relation with the latter. That is to say, a ring
shaped annular gap space 12 in cross section exists between the cover
member 10 and the housing member 9. This annular gap space 12 is formed
around the entire outer peripheries of the air motor 2 and high voltage
generator 7. In order to prevent leak current from the cover member 10 to
the housing member 9, the annular gap space 12 is formed between the
cover member 10 and the housing member 9, for example, in a width greater
than 5 mm.

[0063]Indicated at 13 is a shaping air ring which spurts out shaping air.
This shaping air ring 13 is attached to the front side (the fore side) of
the cover member 10 through the front closing member 11 in such a way as
to circumvent the outer periphery of the rotary atomizing head 3.
Similarly to the cover member 10, the shaping air ring 13 is formed of a
cylindrical shape by use of, for example, PTFE, POM or PET with surfaces
treated with a water repellent agent. A multitude of air outlet holes 13A
are bored in the shaping air ring 13, in communication with a shaping air
passage 14 which is provided in the main housing member 9. Supplying
shaping air through the shaping air passage 14, the air outlet holes 13A
spurts out shaping air toward paint which are sprayed from the rotary
atomizing head 3, for shaping the spray pattern of paint particles
sprayed from the rotary atomizing head 3.

[0064]Denoted at 15 is a high voltage discharge electrode assembly which
is located around the outer periphery of the shaping air ring 13. The
high voltage discharge electrode assembly 15 is composed of support arms
16 and a blade ring 17, which will be described hereinafter.

[0065]Indicated at 16 are support arms which are extended radially outward
from outer periphery of the shaping air ring 13. A plural number of
support arms 16, for example, four support arms 16 are provided at
uniform angular intervals around the shaping air ring 13 to support a
blade ring 17 thereon. Further, the support arms 16 are formed of a
conducting material and electrically connected to the air motor 2 through
a connecting wire 16A.

[0066]Indicated at 17 is the blade ring which is supported on outer distal
ends of the support arms 16. This blade ring 17 is formed substantially
in a round tubular shape by the use of a conducting material like a
metal, for example. Further, the blade ring 17 is constituted by a ring
member 18 which is located on the front side, and a tapered edge portion
19 which is projected in a rearward direction from the ring member 18.
The blade ring 17 is located around the air motor 2 in such a way as to
circumvent the shaping air ring 13.

[0067]In this instance, generally the blade ring 17 is formed as a
circular ring having an inside diameter, for example, approximately 150%
to 250% larger than the outside diameter of the shaping air ring 13, and
a length of 300 mm to 900 mm in the circumferential direction of the
blade ring 17. Further, the blade ring 17 is located substantially in
concentric relation with the rotational shaft 2C of the air motor 2. That
is, at any angular position, the blade ring 17 is kept at the same
distance from the outer periphery of the shaping air ring 13.

[0068]The blade ring 17 is connected to the air motor 2 through connecting
wire 16A and support arms 16. Accordingly, by the high voltage generator
7, a high voltage is applied to the blade ring 17 including the edge
portion 19.

[0069]Indicated at 18 is the ring member which is provided at the front
side of the blade ring 17, and supported on outer distal ends of the
support arms 16 in such a way as to circumvent the shaping air ring 13.
The ring member 18 is rounded in a smooth arcuate shape face at its front
end, on the other hand the ring portion is projected rearward in a thin
blade-like shape at its rear end.

[0070]Designated at 19 is the edge portion which is projected rearward
from the ring member 18 and tapered in the fashion of a thin blade,
forming a sharp edge at the rear end of the blade ring 17. The edge
portion 19 serves to enhance the electric field around the entire body of
the blade ring 17. Therefore, for example, when a high voltage of 90 kV
is applied, a discharge current of 20 μA to 100 μA flows through
the edge portion 19, inducing corona discharge in a stable state.

[0071]Being arranged in the manner as described above, the rotary
atomizing head type coating apparatus of the first embodiment gives the
following performances in a coating operation.

[0072]As the rotary atomizing head 3 of the sprayer unit 1, is put in high
speed rotation by the air motor 2, paint is supplied to the rotary
atomizing head 3 through the feed tube 4. By the rotary atomizing head 3
of the sprayer unit 1 which is in high speed rotation, paint is atomized
and sprayed in the form of finely divided particles under the influence
of centrifugal force. At the same time, shaping air is supplied to the
shaping air ring 13 thereby to control the spray pattern of paint
particles.

[0073]Concurrently, a high voltage is applied to the rotary atomizing head
3 from the high voltage generator 7 through the air motor 2. Therefore,
paint which has been supplied to the rotary atomizing head 3 is imparted
with a high voltage electrostatic charge directly by the rotary atomizing
head 3. Charged paint particles are urged to fly toward and deposit on a
work piece, traveling along an electrostatic field which is formed
between the rotary atomizing head 3 and the work piece.

[0074]Thus, according to the first embodiment, the high voltage discharge
electrode assembly 15 is provided around the outer periphery of the
shaping air ring 13, and a high voltage from the high voltage generator 7
is applied to the blade ring 17 through the air motor 2 and discharged
from the edge portion 19.

[0075]Thus, a high voltage of the same polarity as charged paint particles
is applied to the high voltage discharge electrode assembly 15, inducing
corona discharges and thereby electrifying the cover member 10 with an
electrostatic charge of the same polarity in a positive fashion. Further,
by the high voltage discharge electrode assembly 15, an electrostatic
field of a high voltage is formed around the outer peripheral side of the
cover member 10. Therefore, by the electrostatic field of the high
voltage discharge electrode assembly 15, electrified paint particles are
kept off the cover member 10. Besides, the cover member 10 is imparted
with a high voltage electrostatic charge to prevent deposition of paint
particles.

[0076]On the other hand, by the corona discharge from the edge portion 19
which is extended rearward from entirely around the blade ring 17, the
cover member 10 is imparted with a high voltage electrostatic charge up
to its rear portions, and a high electrostatic potential can be
maintained over broad areas of the cover member 10 to prevent deposition
of charged paint particles.

[0077]Especially in the present embodiment, the blade ring 17 is tapered
to the sharp edge portion 19 in the fashion of a thin blade. Therefore,
an electrostatic field higher than a discharge initiating electrostatic
field, for example, an electrostatic field of approximately 3 kV/m to 5
kV/m can be formed by the edge portion 19. Thus, the edge portion 19
makes it possible obtain a high electric field continuously, permitting
to produce a large quantity of charges in a stabilized state.

[0078]Further, the edge portion 19 is formed entirely around the blade
ring 17, so that it can induce corona discharge on the entire annular
blade ring 17 which circumvents the housing member 9. Therefore, a
sufficient amount of discharge ions is supplied to the cover member 10 on
the exterior side of the housing member 9 to maintain the cover member 10
stably at a high voltage electrostatic potential.

[0079]Furthermore, by the corona discharges from the edge portion 19,
electrostatically attenuated paint particles can be freshly imparted with
an electrostatic charge. As repulsion forces can be generated between the
freshly charged paint particles and the high voltage discharge electrode
assembly 15 or cover member 10, deposition of paint particles on the
cover member 10 can prevent in a more assured manner.

[0080]Moreover, by the use of the edge portion 19, corona discharges can
be induced on the entire annular blade ring 17 which circumvents the
cover member 10. Therefore, the blade ring 17 can be formed in a smaller
size, for example, as compared with an electrode assembly having a number
of acicular electrodes located at intervals around an annular ring member
for corona discharges. Therefore, a sufficient distance can be kept
between the high voltage discharge electrode assembly 15 and a work piece
to prevent occurrence of spark discharges therebetween. It follows that,
even at the time of a coating operation in a narrow space, the atomizer 1
can be moved in a broader range with higher maneuverability.

[0081]Further, according to the first embodiment, the cover member 10 is
fitted around the outer periphery of the housing member 9 and spaced from
the latter by the annular gap space 12. This arrangement reduces contact
areas of the cover member 10 with the housing member 9 which is lower
than air in electric resistance, preventing leaks of electrostatic charge
on the exterior surfaces of the cover member 10 through the housing
member 9 and keeping the cover member 10 in an electrostatically charged
state to prevent deposition of charged paint particles.

[0082]Furthermore, according to the first embodiment, the shaping air ring
13 is described as being formed of an electrically insulating synthetic
resin material. However, the present invention is not limited to a
shaping air ring of this sort. For example, the shaping air ring may be
formed of a conducting metallic material. In this case, a high voltage of
the same potential as paint is applied to the shaping air ring through
the air motor, letting same to act as a repulsive electrode to prevent
deposition of charged paint particles on the shaping air ring.

[0083]Now, turning to FIGS. 5 through 10, there is shown a second
embodiment of the present invention of the rotary atomizing head type
coating apparatus. This second embodiment has features in that a housing
member is composed of a main body portion which is extended in a
longitudinal direction and adapted to hold a paint atomizing means, and a
neck portion which is branched off the main body portion, while a cover
member is composed of a body cover portion enshrouding the main body
portion of the housing member, and a neck cover portion enshrouding the
neck portion of the housing member.

[0084]In the drawings, indicated at 21 is a robot device which is adapted
to carry out a coating operation automatically by the use of a coater
unit which will be described later on. The robot device 21 is largely
constituted by a base 22, and an articulated robot arm (an arm) 23 which
is rotatably and pivotally supported on the base 22. The coater unit 31
is movable relative to a work piece A by the robot device 21, and
connected to the earth ground.

[0085]Indicated at 31 is a cartridge type coater unit which is mounted on
the robot device 21. The coater unit 31 is largely constituted by an
atomizer 32, a housing member 35 and a paint cartridge 42, which will be
described hereinafter.

[0086]Denoted at 32 is an atomizer which sprays atomized paint particles
toward a work piece A which is held at the earth potential. The atomizer
32 is constituted by an air motor 33 and a rotary atomizing head 34 and
the like which will be described hereinafter.

[0087]Indicated at 33 is an air motor which is formed of a conducting
metallic material. This air motor 33 is constituted by a motor housing
33A, a rotational shaft 33C which is rotatably supported within the motor
housing 33A through a static air bearing 33B, and an air turbine 33D
which is fixedly mounted on a base end portion of the rotational shaft
33C. Upon supplying drive air to the air turbine 33D through an air
passage 39 which will be described hereinafter, the rotational shaft 33C
of the air motor 33 is put in high speed rotation, for example, rotated
at a speed of 3,000 to 100,000 r.p.m together with the rotary atomizing
head 34.

[0088]Indicated at 34 is a rotary atomizing head which is mounted on a
fore end portion of the rotational shaft 33C of the air motor 33. This
rotary atomizing head 34 is formed of, for example, a conducting metallic
material or conducting synthetic resin material. Through a feed tube 44
which will be described hereinafter, paint is supplied to the rotary
atomizing head 34 which is put in high speed rotation by the air motor,
and atomized paint particles are sprayed forward from a paint releasing
edges 34A at the fore end of the rotary atomizing head 34 under the
influence of centrifugal force. Further, the rotary atomizing head 34 is
connected to a high voltage generator 45 through the air motor 33, which
will be described after. Therefore, during an electrostatic coating
operation, a high voltage is applied to the rotary atomizing head 34 as a
whole to apply a high voltage electrostatic charge directly to paint
which is flowing on surfaces of the rotary atomizing head 34.

[0089]Indicated at 35 is a housing member which holds the air motor 33 in
position. Similarly to the housing member 9 in the foregoing first
embodiment, this housing member 35 is formed of an electrically
insulating synthetic resin material, for example, such as POM
(polyoxymethylene), PET (polyethylene terephthalate), PEN (polyethylene
naphthalate), PP (polypropylene), HP-PE (high-pressure polyethylene),
HP-PVC (high-pressure polyvinylchloride), PEI (polyether imide), PES
(polyether sulfon), polymethyl pentene and the like.

[0090]The housing member 35 is composed of a longitudinally extending
cylindrical main body portion 36, and a neck portion 37 which is branched
off from an axially intermediate portion of the main body portion 36 and
extended obliquely in a rearward direction.

[0091]Formed into the fore end of the main body portion 36 is a motor
receptacle hole 36A which is adapted to accommodate the air motor 33,
while formed into the rear end of the main body portion 36 is a container
receptacle hole 36B which is adapted to accommodate a container 43 of a
paint cartridge 42, which will be described hereinafter. Further, a feed
tube passage hole 36C is formed axially in the main body portion 36
through centers of the motor receptacle hole 36A and container receptacle
hole 36B.

[0092]On the other hand, a generator receptacle hole 37A is provided in
the neck portion 37 to accommodate a high voltage generator 45 which will
be described later on. Base end of the neck portion 37 is attached to the
fore end of the robot arm 23 of the robot device 21 through a tubular
connector member 38 which is formed of an electrically insulating
synthetic resin material. Further, an air passage 39 is formed internally
of the housing member 35 to supply drive air to the air motor 33, along
with an extruding liquid passage 40 which supplies an extruding liquid to
a paint cartridge 42 for controlling a flow rate of paint as described in
greater detail hereinafter.

[0093]Denoted at 41 is a shaping air ring which is provided on the front
side of the main body portion 36 of the housing member 35 in such a way
as to circumvent the rotary atomizing head 34. This shaping air ring 41
is formed, for example, by the use of a conducting metallic material, and
electrically connected to the air motor 33. A plural number of air outlet
holes 41A bore in the shaping air ring 41 to spurt out shaping air toward
paint particles sprayed from the rotary atomizing head 34.

[0094]Indicated at 42 is a paint cartridge which supplies paint to the
rotary atomizing head 34. This paint cartridge 42 is largely constituted
by a container 43 in the form of an axially extending tubular
(cylindrical) casing, a feed tube 44 which is extended axially forward
from the container 43, and a piston which defines a paint chamber and an
extruding liquid chamber (both not shown) within the casing of the
container 43.

[0095]The paint cartridge 42 is set in a container receptacle hole 36B at
the rear end of the housing member 35, after inserting the feed tube 44
in the feed tube passage hole 36C. At the time of a coating operation, an
extruding liquid is supplied to the extruding liquid chamber through the
extruding liquid passage 40 in the housing member 35, displacing the
piston forward and thereby forcing paint to flow into the feed tube 44
from the container 43 for supply to the rotary atomizing head 34. At the
time of refilling the paint cartridge 42, it is detached from the
container receptacle hole 36B and connected to a paint replenisher (not
shown) to refill paint into the paint chamber in the container 43 through
the feed tube 44.

[0096]Indicated at 45 is a high voltage generator which is accommodated in
the neck portion 37 of the housing member 35 as a high voltage
application means. Input side of this high voltage generator 45 is
connected to an external high voltage controller 46 through the robot
device 21, and its output side is connected to the air motor 33. For
example, the high voltage generator 45 is a multi-stage rectification
circuit (i.e., so-called Cockcroft circuit) which is constituted by a
plurality of capacitors and diodes.

[0097]The high voltage generator 45 generates, for example, a high voltage
of -30 kV to 150 kV by elevating a DC source voltage which supplied from
the high voltage controller 46. The output level (the high voltage
output) of the high voltage generator 45 is determined depending upon the
level of the source voltage which is supplied from the high voltage
controller 46, that is to say, controlled by the level of the source
voltage from the high voltage controller 46. By the high voltage
generator 45, paint is directly imparted with a high voltage
electrostatic charge by way of the air motor 33 and rotary atomizing head
34 through high voltage cable 45A.

[0098]Indicated at 47 is a cover member enshrouding outer surfaces of the
housing member 35. This cover member 47 is formed by the use of a
fluorine-base synthetic resin material which is high in resistance and
non-water-absorptive, for example, by the use of a film or sheet of
fluorine-base synthetic resin material such as PTFE
(polytetrafluoroethylene) and ETFE (a copolymer of ethylene and
tetrafluoroethylene). Further, the cover member 47 is composed of a body
cover 48 enshrouding the outer surface 36D of the main body portion 36,
and a neck cover 49 enshrouding the outer surface 37B of the neck portion
37. The respective covers 48 and 49 are each formed, for example, by
rolling a synthetic resin film having a thickness of 0.1 mm to 5 mm into
a tubular shape.

[0099]In this instance, the body cover 48 is extended rearward of the main
body portion 36, covering not only the outer surface 36D of the main body
portion 36 but also the outer surfaces of the container 43 of the paint
cartridge 42. The body cover 48 is fitted on annular flanges 50 which are
provided in opposite front and rear end portions of the main body 36. On
the other hand, the neck cover 49 is fitted on an annular flange 51,
which is provided at a longitudinally intermediate position on the neck
portion 37, and on the connector member 38 which is provided at a lower
distal end of the neck portion 37.

[0100]Except small surface areas which are in contact with the flanges 50,
almost the entire inner surface of the body cover 48 which confronts face
to face with the outer surface 36D of the main body portion 36 is spaced
away from and kept out of contact with the latter. Similarly, except
small surface areas which are in contact with the flange 51 and connector
member 38, almost the entire inner surface of the neck cover 49 which
confronts face to face with the outer surface 37B of the neck portion 37
is spaced away from and kept out of contact with the latter.

[0101]As a consequence, the main body portion 36 and the body cover 48 are
intervened by an annular gap space 52 of an annular shape in cross
section, and similarly the neck portion 37 and neck cover 49 are
intervened by an annular gap space 52 of an annular shape in cross
section. Thus, the cover member 47 and housing member 35 are intervened
by an annular gap space 52 almost in entire areas. Consequently, on the
outer peripheral side, the air motor 33 and high voltage generator 45 are
surrounded by the annular gap space 52 substantially in entire areas. The
annular gap spaces 52 are formed between the cover member 47 and housing
member 35, for example, in a width of 5 mm or more in order to prevent
leak current from the cover member 47 to the housing member 35.

[0102]Designated at 53 is a high voltage discharge electrode assembly
which is located around the outer periphery of the shaping air ring 41.
This high voltage discharge electrode assembly 53 is composed of support
arms 54, blade ring 55 and edge portions 56, 57 and 58, which will be
described hereinafter.

[0103]Indicated at 54 are support arms which are extended radially outward
from the outer periphery of the shaping air ring 41. More specifically,
the support arms 54 are extended radially outward from the side of the
housing member 35 as far as a position on the outer peripheral side
(radially outward) of the body cover 48. For example, three support arms
54 are provided at uniform angular intervals around the shaping air ring
41 to support the blade ring 55 thereon.

[0104]Indicated at 55 is a blade ring which is supported on outer distal
ends of the support arms 54. This blade ring 55 is formed substantially
in a tubular shape, for example, by the use of conducting material like a
metal. Further, the blade ring 55 is provided with fore and rear blade
portions 55A and 55B which are projected in forward and rearward
directions, respectively, and an annular outer flange portion 55C which
is projected in a radially outward direction. Moreover, the blade ring 55
is located around the air motor 33 in such a way as to circumvent a front
portion of the body cover 48.

[0105]In this instance, the blade ring 55 is in the form of a circular
ring having an outside diameter which is, for example, 150% to 200%
larger than outside diameter of the body cover 48, and having a length of
approximately 300 mm to 900 mm in the circumferential direction. Further,
the blade ring 55 is positioned substantially in concentric relation with
the rotational shaft 33C of the air motor 33. Thus, the blade ring 55 is
kept at a constant distance from the body cover 48 at any angular
position around its body.

[0106]Further, the blade ring 55 is connected to the air motor 33 through
the support arms 54 and shaping air ring 41. Therefore, a high voltage is
applied to the blade ring 55 from the high voltage generator 45.

[0107]Indicated at 56, 57 and 58 are edge portions which are provided at
outer distal ends of the fore and rear blade portions 55A and 55B and the
flange portion 55C, respectively. In this instance, the front edge
portion 56 is formed by gradually reducing the thickness of the fore
blade portion 55A in the forward direction in the fashion of a thin
blade. Similarly, the back edge portion 57 is formed by gradually
reducing the thickness of the rear blade portion 55B in the rearward
direction in the fashion of a thin blade. Further, the top edge portion
58 is formed by gradually reducing the thickness of the outer flange
portion 55C in a radially outward direction.

[0108]The front, back and top edge portions 56, 57 and 58 serve to
intensify the electric field all around the blade ring 55. For example,
when a high voltage of 90 kV is applied to the edge portions 56 to 58, a
discharge current of 20 μA to 100 μA flows through the edge
portions 56 to 58, inducing corona discharge in a stabilized state.

[0109]Being arranged in the manner as described above, the rotary
atomizing head type coating apparatus of the second embodiment gives the
following performances as a coating apparatus.

[0110]As a work piece A is located in the vicinity of the robot device 21
by a conveyer, or the like, the robot device 21 is put in a playback
action according to pre-loaded teaching actions in a memory, bringing the
coater unit 31 to an operative position relative to the work piece A.

[0111]At this time, the rotary atomizing head 34 on the coater unit 31 is
put in high speed rotation by the air motor 33, and paint is supplied to
the rotary atomizing head 34 from the container 43 through the feed tube
44. Under the influence of centrifugal force resulting from high speed
rotation of the rotary atomizing head 34, paint is sprayed forward in the
form of finely divided particles by the coater unit 31. Concurrently,
shaping air is spurted out from the shaping air ring 41 to control the
spray pattern of paint particles.

[0112]At the same time, a high voltage is applied to the rotary atomizing
head 34 from the high voltage generator 45 through the air motor 33.
Accordingly, the paint which has been supplied to the rotary atomizing
head 34 is directly charged with a high voltage by the rotary atomizing
head 34 and sprayed in the form of charged paint particles. The charged
paint particles are urged to fly toward and deposit on a work piece A
which is held at the earth potential, traveling along an electrostatic
field which is formed between the rotary atomizing head 34 and the work
piece A.

[0113]Thus, according to the second embodiment, the high voltage discharge
electrode assembly 53 is provided around the outer periphery of the body
cover 48, applying a high voltage to the blade ring 55 from the high
voltage generator 45 through the air motor 33 and shaping air ring 41 and
letting the blade ring 55 discharge the high voltage from the front and
back edge portions 56 and 57 and the top edge portion 58 as well. Thus,
ions of the same polarity as the charged paint particles are discharged
by the use of the high voltage discharge electrode assembly 53, while
imparting an electrostatic charge of the same polarity to the cover
member 47.

[0114]In addition, a high voltage electrostatic field can be formed around
the outer periphery of the cover member 47 by the blade ring 55. Thus,
the electrostatic field of the blade ring 55 contributes to keep charged
paint particles off the cover member 47, imparting a high voltage
electrostatic charge to the cover member 47 to prevent deposition of
charged paint particles.

[0115]Furthermore, since the blade ring 55 is arranged to circumvent the
body cover 48, as compared with the case of excluding the high voltage
discharge electrode assembly 53, it can impart a high voltage
electrostatic charge to broader areas of the cover member 47 from entire
part of blade ring 55, thus preventing deposition of charged paint
particles in broader areas at the cover member 47.

[0116]In this connection, if a discharge ring without an edge were used,
the strongest discharge would occur at a point which is closest to a
grounded body. In such a case, it is very likely that only weak
discharges take place at other points under the influence of electron
clouds resulting from the strong discharge.

[0117]In contrast, according to the second embodiment of the invention,
the blade ring 55 is provided with edge portions 56 to 58 each in the
shape of a sharp blade edge. Therefore, an extremely strong electric
field which is higher than a discharge initiating electric field, for
example, an electric field of 3 kV/m to 5 kV/m can be secured at the
respective edge portions 56 to 58, thereby suppressing strong discharges
which might occur to part of the blade ring 55 on approach to a coating
object (a grounded object) and inducing stabilized discharge all around
the blade ring 55 by way of the edge portions 56 to 58.

[0118]Further, since the edge portions 56 to 58 are formed all around the
blade ring 55, corona discharges take place on the entire annular body of
the blade ring 55 which circumvents the cover member 47. Accordingly, a
sufficient amount of discharge ions can be supplied to the cover member
47 for maintaining same at a high electrostatic potential in a stabilized
state.

[0119]Besides, the corona discharges at the edge portions 56 to 58 play
the role of recharging paint particles with an attenuated amount of
electrostatic charge. Consequently, a repulsion force occurs between
recharged paint particles and the blade ring 55 or the cover member 47 to
prevent deposition of paint particles on the cover member 47 in a more
assured manner.

[0120]Furthermore, since corona discharges can be induced by the edge
portions 56 to 58 on and around the entire annular body of the blade ring
55 which circumvents the cover member 47, it is possible to downsize the
blade ring 55 as compared with a blade ring which is arranged to induce
corona discharges at part of its annular body. As a result, it becomes
possible to keep the blade ring 55 at a sufficient distance from a work
piece A to prevent corona discharges between them. Accordingly, even in a
coating operation in a narrow space, the atomizer 32 can be moved in a
broader range with higher maneuverability.

[0121]In addition to the fore and rear blade portions 55A and 55B, the
blade ring 55 is provided with the outer flange portion 55C which is
extended radially outward, and edge portions 56 to 58 in the shape of a
thin blade edge are formed on these fore and rear blade portions 55A and
55B and the outer flange portion 55C. Therefore, electric field can be
concentrated not only at the edge portions 56 and 57 on the fore and rear
blade portions 55A and 55B but also at the edge portion 58 on the outer
flange portion 55C induce corona discharge. Therefore, a sufficient
amount of discharge ions can be supplied to the cover member 47, while
accelerating recharging of paint particles.

[0122]Furthermore, according to the second embodiment, the housing member
35 is enshrouded by the cover member 47, and the annular gap space 52 is
provided between the housing member 35 and the cover member 47.
Therefore, by the provision of the annular gap space 52, contacting areas
of the housing member 35 with the cover member 47 can be reduced to
suppress leaks of electrostatic charge on the exterior surface of the
cover member 47 through the housing member 35, maintaining the cover
member 47 in an electrostatically charged state to prevent deposition of
paint particles.

[0123]Now, turning to FIGS. 11 to 13, there is shown a rotary atomizing
head type coating apparatus according to a third embodiment of the
present invention. This third embodiment has a feature in that a number
of notches are provided at intervals around the edge portion of the
entire blade ring. In the following description of the third embodiments,
those component parts which are identical with counterparts in the
foregoing first embodiments are simply designated by the same reference
numerals or characters to avoid repetitions of similar explanations.

[0124]Indicated at 61 is a high voltage discharge electrode assembly which
is provided around the outer periphery of a shaping air ring 41. This
high voltage discharge electrode assembly 61 is composed of support arms
62, blade ring 63, edge portions 64 to 66 and notches 67 to 69, which
will be described hereinafter.

[0125]Indicated at 62 are a number of support arms which are extended
radially outward of a shaping air ring 41. These support arms 62 are
extended radially outward from the outer periphery of the housing member
35 to a point outward of the outer periphery of a body cover 48. In this
case, for example, three support arms 62 are provided at uniform angular
intervals around the shaping air ring 41 to support a blade ring 63
thereon.

[0126]Indicated at 63 is a blade ring which are supported on outer distal
ends of the radial support arms 62. Substantially in the same way as the
blade ring 55 in the foregoing second embodiment, this blade ring 63 is
formed in the shape of a circular ring by the use of a conducting
material like a metal, for example. Further, the blade ring 63 is
provided with fore and rear blade portions 63A and 63B which are
projected in forward and rearward directions, respectively, and a
ring-like outer flange portion 63C which is projected radially outward on
the circumference of the blade ring 63. Further, the blade ring 63 is so
located as to circumvent a front side portion of the body cover 48, and
connected to a high voltage generator 45 through the support arms 54 and
shaping air ring 41. Accordingly, a high voltage is applied to the blade
ring 63 from the high voltage generator 45.

[0127]Indicated at 64, 65 and 66 are edge portions which are provided on
the fore and rear blade portions 63A and 63B and the outer flange portion
63C of the blade ring 63.

[0128]In this instance, a front edge portion 64 is formed by gradually
reducing the thickness of the fore blade portion 63A in the forward
direction in the fashion of a sharp thin blade. Moreover, the front edge
portion 64 is divided into a number of front edge sections (ten front
edge sections in the case of the third embodiment shown) by adjacent
notches 67.

[0129]A rear edge portion 65 is formed by gradually reducing the thickness
of the rear blade portion 63B in the fashion of a sharp thin blade, and
divided into ten rear edge sections. Further, an outer edge portion 66 is
formed by gradually reducing the thickness of the outer flange portion
63C in a radially outward direction in the fashion of a sharp thin blade,
and divided into ten outer edge sections.

[0130]The front, rear and outer edge portions 64 to 66 function to
intensify electric field around the circular body of the blade ring 63.
For example, when a high voltage of 90 kV is applied, a discharge current
of approximately 20 μA to 100 μA flows through each one of the edge
portions 64 to 66 to induce stabilized corona discharge.

[0131]Indicated at 67 to 69 are a plural number of notches which are
formed in the edge portions 64 to 66 at intervals in the circumferential
direction of the blade ring 63. In the case of the particular embodiment
shown, the notches 67 to 69, for example, ten notches are formed in the
edge portions 64 to 66 at uniform intervals in the circumferential
direction of the blade ring 63.

[0132]In this instance, each one of the notches 67 is formed in an arcuate
shape and extended in a circumferential direction along the front edge
portions 64. Further, a plural number of notches 67 (ten notches in the
case of the third embodiment shown) are formed at uniform intervals in
the circumferential direction between adjacent front edge portions 64. By
the provision of the notches 67, an electric field is further
concentrated at the opposite ends 64A of the front edge portions 64 to
accelerate discharge.

[0133]Similarly, ten notches 68 are formed at uniform intervals in the
circumferential direction between front edge portions 65 to further
concentrate an electric field at the opposite ends of the edge sections
65A. Moreover, ten notches 69 are formed at uniform intervals in the
circumferential direction between outer edge portions 66 to further
concentrate an electric field at the opposite ends 66A of the latter.

[0134]In a case where the respective notches are small in length L in the
circumferential direction, ion clouds resulting from discharging can act
as a pseudo-electrode, conversely suppressing the discharge by easing the
intensity of an electric field. Therefore, in the present embodiment, the
notches 67 to 69 are formed to have a sufficiently large length as
compared to the intervals of corona clouds, for example, a length L
greater than 20 mm.

[0135]Thus, the third embodiment can produce the same operational effects
as the foregoing second embodiment. Especially in the case of the third
embodiment, notches 67 to 69 are formed in the edge portions 64 to 66,
respectively, to further concentrate an electric field at the opposite
ends of the respective edge sections, which are at the opposite sides of
the notches 67 to 69 in the circumferential direction. Thus, the notches
make discharges take place more easily at the edges 64A to 66A,
encouraging corona discharges at the edge portions 64 to 66.

[0136]Now, turning to FIGS. 14 to 17, there is shown a rotary atomizing
head type coating apparatus according to a fourth embodiment of the
present invention. This fourth embodiment has a feature in the provision
of a star ring which is bent at a plural number of points alternately
toward and away from a housing member. In the following description of
the fourth embodiment, those component parts which are identical with
counterparts in the foregoing second embodiment are simply designated by
the same reference numerals or characters to avoid repetitions of similar
explanations.

[0137]Indicated at 71 is a high voltage discharge electrode assembly which
is located around the outer periphery of a shaping air ring 41. This high
voltage discharge electrode assembly 71 is composed of support arms 72
and a star ring 73, which will be described hereinafter.

[0138]Denoted at 72 are support arms which are provided around the outer
periphery of the shaping air ring 41. These support arms 72 are extended
radially outward from the side of the housing member 35 to a point
outward of the outer periphery of the body cover 48. In the particular
embodiment shown, for example, three support arms 72 are located in
equidistant angular positions around the outer periphery of the shaping
air ring 41 to support a star ring 73.

[0139]Indicated at 73 is a star ring which is formed in the shape of a
star and provided on the front edge of the support arm 72, for example,
by the use of a conducting wire like a metal wire. In this regard, it is
preferable to form the star ring 73, for example, by the use of a spring
steel wire so that it is deformable when it comes into contact with a
worker or other object but it can restore its shape by itself afterwards.
Further, the diameter of the wire to be used for the star ring 73 should
be of a gauge suitable for securing a discharge initiating electric field
in addition to shape retainability, for example, should be preferably in
the range of from 0.3 mm to 5 mm.

[0140]The star ring 73 is formed by bending a wire at a plural number of
points alternately in inward and outward directions toward and away from
the cover member 47 and in the shape of a ring. Thus, the star ring 73
contains alternately a inward bend portion 73A which is located closer to
the cover member 47, and an outward bend portions 73B which is located
away from the cover member 47. Moreover, for example, fifteen bend
portions 73A, 73B are each provided alternately at uniform intervals in
the circumferential direction.

[0141]In this instance, the inward bend portions 73A in adjacent positions
spaced away from each other by a distance L which is substantially larger
than an interval between corona clouds, for example, by a distance L
larger than 20 mm. Similarly, the outward bend portions 73B in adjacent
positions are spaced away from each other by a distance L larger than 20
mm. Thus, the inward and outward bend portions 73A and 73B serve to
concentrate an electric field furthermore.

[0142]In this connection, the wire diameter of the star ring 73 and
discharge initiating electric field are in the relations as discussed
below.

[0143]In the first place, as shown in FIG. 17, assuming that a wire is a
cylinder of an infinite length, a cylinder of a radius r is located in a
position which is spaced from a flat plate (a work piece A) at the earth
potential by a spatial insulating distanced. At this time, an electric
field E which is formed around the cylinder (wire) is expressed as
(E=η×E0), that is, as a value which is obtained by multiplying
an electric field concentration coefficient η of Equation (1) below
by a mean electric field E0.

η×× ##EQU00001##

[0144]In this instance, if a voltage of 60 kV is applied to the star ring
73 and the distance d between the star ring 73 and a work piece A is 300
mm, the mean electric field E0 between the star ring 73 and the work
piece A is 0.2 kV/mm. On the other hand, a discharge initiating electric
field, which starts a corona discharge in standard atmospheric air, is
approximately 3 kV/mm. Therefore, in order to induce stable and
continuous corona discharge in an assured way despite variations in the
distance d to the work piece A and in the applied voltage to the star
ring 73, the electric field to be formed around the star ring 73 is
preferred to be at least three times higher than the discharge initiating
electric field, that is, to be as strong as 9 kV/mm or more.

[0145]Thus, in order to maintain around the star ring 73 an electric field
which is at least three times as strong as the discharge initiating
electric field, the electric field concentration coefficient η should
be set at 45 or at a greater value. In this regard, since the wire radius
r in Equation (1) above needs to be set at 1.05 mm or at a smaller value,
the wire diameter should be 2.1 mm or smaller.

[0146]The smaller the wire diameter of the star ring 73, the higher the
intensity of electric field but lower in mechanical strength. Further,
even if the wire diameter is increased, an electric field of a strength
three times as high as a discharge initiating electric field can be
formed around the star ring 73 by increasing the value of the high
voltage to be applied to the star ring 73. Gathering from these
observations, the wire diameter of the star ring 73 is set in the range
of approximately 0.3 mm to 5 mm in the present embodiment.

[0147]Thus, the fourth embodiment can produce substantially the same
operational effects as the foregoing second embodiment. Especially in the
case of the fourth embodiment, the star ring 73 which is alternately bent
in inward and outward directions toward and away from the cover member 47
is provided to concentrate an electric field at the bent portions 73A and
73B. That is, discharges take place more easily at the bent portions 73A
and 73B of the star ring 73, accelerating corona discharges from the bent
portions 73A and 74B.

[0148]Further, since the wire diameter of the star ring 73 is in the range
of from 0.3 mm to 5 mm, the electric field for the star ring 73 as a
whole can be intensified to a level higher than a discharge initiating
electric field, making the entire star ring 73 a high electric field.
Therefore, corona discharge can be induced on the entire star ring 73 to
supply a sufficient amount of discharge ions to the cover member 47 while
at the same time recharging paint particles.

[0149]Turning now to FIGS. 18 to 20, there is shown a rotary atomizing
head type coating apparatus according to a fifth embodiment of the
present invention. This fifth embodiment has a feature in the provision
of a helical ring which is helically wound in such a way as to circumvent
a housing member in circumferential direction. In the following
description of the fifth embodiments, those component parts, which are
identical with counterparts in the foregoing second embodiments, are
simply designated by the same reference numerals or characters to avoid
repetitions of similar explanations.

[0150]Indicated at 81 is a high voltage discharge electrode assembly which
is located around the outer periphery of the shaping air ring 41. This
high voltage discharge electrode assembly 81 is composed of support arms
82, helical ring 83 and so on, which will be described hereinafter.

[0151]Indicated at 82 are support arms which are extended radially outward
from the outer periphery of the shaping air ring 41. More specifically,
the support arms 82 are extended radially outward from the side of the
housing member 35 as far as a position on the outer peripheral side
(radially outward) of the body cover 48. For example, three support arms
82 are provided at uniform angular intervals around the shaping air ring
41 to support the helical ring 83 thereon.

[0152]Indicated at 83 is a helical ring 83 which are supported on outer
distal ends of the support arms 82. This helical ring 83 is formed
substantially in a ring shape, for example, by use of conducting material
like a metal wound 18 times in helical shape (coil shape) while using a
said wire. Further, the diameter of the wire to be used for the helical
ring 83 should be of a gauge suitable for securing a discharge initiating
electric field in addition to shape retainability, for example, should be
preferably in the range of from 0.3 mm to 5 mm, similar to the star ring
73 in the forth embodiment. Moreover, the length of each turn pitch
(distance L) of the helical ring 83 is spaced away from each other and it
is substantially larger than a interval between corona clouds, for
example, by a distance L larger than 20 mm.

[0153]Thus, the fifth embodiment can produce the same operational effects
as the foregoing second and forth embodiments. Especially in the case of
the fifth embodiment, helical ring 83 is constructed by wire wound in
circumferential direction to circumvent body cover 48. The use of a
helical ring 83 permit to provide a high voltage discharge electrode
assembly 81 in a more compact form in outer configuration, and to
increase the wire length of the helical ring 83. Since corona discharges
can be induced on the entire wire which is elongated in length, it
becomes possible to downsize a high voltage discharge electrode assembly
81 in a compact form and increase the amount of discharge ions.

[0154]A conducting shaping air ring 41 is employed in the second to fifth
embodiment described above. However, if desired, it is possible to attach
an insulating shaping air ring in place of the conducting shaping air
ring as in the first embodiment.

[0155]Further, in the second to fifth embodiment, a high voltage discharge
electrode assembly 53, 61, 71 or 81 is applied to a rotary atomizing head
type coating apparatus with a housing member 35 which is composed of a
main body portion 36 and a neck portion 37. However, the present
invention is not limited to this feature, and the high voltage discharge
electrode assemblies 53, 61, 71 and 81 of the second to fifth embodiments
may be applied to a rotary atomizing head type coating apparatus with a
housing member without a neck portion like the housing member 9 in the
first embodiment. If desired, the high voltage discharge electrode
assembly 15 of the first embodiment may be applied to a rotary atomizing
head type coating apparatus as in the second embodiment.

[0156]Furthermore, in the second and third embodiment, an outer flange
portion 55C, 63C is provided on the outer periphery of a blade ring 55,
63 of high voltage discharge electrode assembly 53, 61. However, the
outer flange portion 55C or 63C may be omitted if desired. In the second
and third embodiment, one of or both of front and rear blade portions 55A
and 55B or 63A and 63B of the blade ring 55 or 63 may be omitted if
desired.

[0157]Moreover, in each one of the foregoing embodiments, the cover member
10, 47 may be is provided around the housing member 9, 35, yet may be
omitted if necessary. In such a case, an electrostatic charge is imparted
to exterior surfaces of the housing member 9, 35 instead of the cover
member 10, 47 by corona discharge from high voltage discharge electrode
assembly 15, 53, 61, 71, 81.

[0158]Further, in each one of the foregoing embodiments, the present
invention is applied to a rotary atomizing head type coating apparatus (a
rotary atomizing head type electrostatic coating apparatus) which is
equipped with a rotary atomizing head 3, 34 for atomizing and spraying
paint. However, the present invention is not limited to an electrostatic
coating apparatus of this sort, and can be similarly applied to other
electrostatic coating apparatus such as pneumatic atomization type
electrostatic coating apparatus and hydraulic atomization type
electrostatic coating apparatuses as well.